Manholes are used to provide street-level access to sewer lines and other underground structures. Most often, the top portion of the manhole has the form of a cylindrical frame (or casting) with a lid. The lower portion of the casting, which is not generally seen after installation, often resembles a hat with a brim. This hat-shaped casting rests on a concrete cone leading to a sewer line. The upper portion of the casting defines an opening that may be closed with a lid. The elevation of the manhole casting and lid may be raised to the level of the surrounding surface grade by placing one or more concrete adjusting rings between the bottom of the casting and the cone. A manhole structure is thus created by stacking a number of components on top of each other. After the manhole structure is installed, the space around it is typically filled in with earth so that the lid at the top portion of the manhole casting is conveniently accessible at street-level.
Manholes created by such stacking of components are vulnerable to leaks. Water and other contaminants may enter through gaps between the stacked components after installation. Once the manhole structure has been installed and earth has been filled in around it, gaps below the ground level become difficult to reach. It is thus desirable to seal the manhole structure during installation to prevent future leaks at the interfaces between the stacked components.
Various methods and devices are known for sealing the external surfaces of manhole structures. One method employs an elastomeric band positioned around the top portion of the cone and extending over the adjusting rings to the base of the manhole casting. Because the cone and the adjusting rings have generally the same outer perimeter, one or more sealing bands may be used to provide an external seal for the gaps between these components. A band extends over the cone (and any adjusting rings) to the casting base as in U.S. Pat. No. 5,876,533 or may extend in tapered form to the upper portion of the casting as in U.S. Pat. No. 7,150,580.
To reduce the risk of accumulating water or contaminants between the inner layer of the seal and the outer layer of the manhole, methods have been devised for keeping the external seal snugly fitted to the manhole structure. A heat-sealing method, for example, is known whereby the sealing band is heated before fitting so that it may be secured tightly to the manhole structure, thereby reducing bulges and air pockets. But methods that use heat require a heat source, often torches and other special tools that involve hazards to the user.
What is needed in the industry is a device and method for sealing a manhole structure so that the seal is retained in close proximity to the external surfaces of manhole structure without the use of heat-sealing methods.